Mode of Transmission of Vibriosis among AyuPlecoglossus altivelis

The mode of transmission of Vibrio anguillarum infection in ayu (Plecoglossus altivelis) and the portal of entry for the pathogen were investigated by the use of various challenge methods. The methods employed were immersion, direct contact, cohabitation, patch contact (filter paper soaked in bacterial suspension placed on part of a test fish for 1 min), and intubation. Based on the results of immersion, direct contact, and cohabitation challenges, it was concluded that water-borne infection is the primary mode of transmission of the disease. The patch contact challenge revealed that V. anguillarum penetrated the host through the skin, fins, anus, and gills. Among those, the skin and anus were determined to be the essential portals of entry for the pathogen. Artificial wounds of the skin surface caused by swabbing or scale removal facilitated invasion by the pathogen. Infection also was established by oral and anal intubations.